Building walls may be insulated by injecting plastic foam into them through injection holes uniformly spaced over the wall. Upon completion of the injection foaming process, the injection holes need to be closed in a manner that is esthetically pleasing. Accordingly, a wall plug is desired that will be retained in the injection hole, be inexpensive to produce, and attractive in appearance by blending into the wall surface. If desired, the wall plugs should be of a material that may be painted over when the entire wall surface is being painted.